1. Field of the Invention
The present invention relates to an ONT management control protocol in a gigabit-capable passive optical network (hereinafter, simply referred to as ‘GPON’).
2. Description of the Related Art
In order to construct access networks from a telephone office to a building and a home, there have been recent suggestions regarding various types of network structures, and methods for improving the existing various network structures. For example, the various network structures and the methods for improving the various network structures include xDSL (x-Digital Subscriber Line), HFC (Hybrid Fiber Coax), FTTB (Fiber To The Building), FTTC (Fiber To The Curb), FTTH (Fiber To The Home) and so forth. Among them, the FTTx (x=B, C, H) can be classified into an active FTTx embodied as a structure of an active optical network (hereinafter, simply referred to as ‘AON’) and a passive FTTx embodied as a structure of a passive optical network (hereinafter, referred to as ‘PON’).
The relationship of PONs with that of passive FTTxs has a point-to-multipoint topology using passive elements. Due to this relationship, the PON has been suggested as a scheme for constructing future access networks having improved economical efficiency as compared with other types of access networks. For example, in the PON, one optical line termination (hereinafter, simply referred to as ‘OLT’) is connected to a plurality of optical network units (hereinafter, simply referred to as ‘ONUs’) by using a 1×N passive optical distribution network (hereinafter, simply referred to as ‘ODN’), thereby constructing a distribution topology having a tree structure.
Additional, with regard to PONs, an asynchronous transfer mode-passive optical network (hereinafter, simply referred to as ‘ATM-PON’) has been initially developed and standardized. Standardized contents about the ATM-PON have been described in ITU-T G.982, ITU-T G983.1, and ITU-T G.983.3 issued by ITU-T (International Telecommunication Union-Telecommunication section). Moreover, a standardization work for a gigabit-capable passive optical network (hereinafter, simply referred to as ‘GPON’) is still being carried out by the ITU-T.
FIG. 1 shows a structure of a conventional PON. The conventional PON includes one OLT 10 and a plurality of ONUs. As shown in FIG. 1, one OLT 10 is connected to three ONUs 12a, 12b, and 12c by means of an ODN 16.
Referring to FIG. 1, the OLT 10 is positioned at a root of a tree structure and has a main function of providing information to subscribers of access networks. The ODN 16 is connected to the OLT 10 and has a tree topology. Also, the ODN 16 distributes downstream data frames transmitted from the OLT 10 to the ONUs 12a, 12b and 12c and transfers upstream data frames transmitted from the ONUs 12a, 12b and 12c to the OLT 10 by multiplexing the upstream data frames. Meanwhile, the ONUs 12a, 12b, and 12c receive the downstream data frames to provide the downstream data frames to terminal users 14a, 14b, and 14c. In addition, the ONUs 12a, 12b, and 12c transfer data outputted from the terminal end users 14a, 14b, and 14c as the upstream data frames to the OLT 10 through the ODN 16. At this time, the terminal users 14a, 14b, and 14c connected to the ONUs 12a, 12b, and 12c, respectively, signify various kinds of access network terminal apparatuses which can be used in the PON having an NT (Network Terminal).
In general, the data frame used for transmission in an ATM-PON includes ATM cells having a size of 53 bytes packaged in a predetermined size is upwardly or downwardly transmitted in the ATM-PON. In the PON having the tree structure shown in FIG. 1, the OLT 10 appropriately inserts downstream cells to be distributed to each of the ONUs 12a, 12b, and 12c into a downstream frame. Also, when performing the upstream transmission, the OLT 10 accesses data transferred from the ONUs 12a, 12b, and 12c using a TDM (Time Division Multiplexing) method. At this time, since the OLT 10 is connected to the ONUs 12a, 12b, and 12c by means of the ODN 16, which is a passive element, the OLT 10 prevents data from colliding with each other in the ODN 16 by using a virtual distance correction algorithm, which is called “ranging”. In addition, when performing the downstream transmission to the ONUs 12a, 12b, and 12c from the OLT 10, the OLT 10 exchanges with the ONUs 12a, 12b and 12c an encryption key, which is used for encrypting data in order to maintain security, and an OAM (Operations, Administration and Maintenance) message, which is used for maintenance and management. Accordingly, a dedicated ATM cell or a data field within a general ATM cell for exchanging messages by a predetermined interval is provided in the upstream/downstream frame.
A broadband passive optical network (hereinafter, referred to as ‘BPON’) that is based on the G.983 series, which has been already standardized as described above, operates on the basis of ATM. However, the GPON supports a transfer mode based on cells which deals with ATM services (called ‘ATM’). Also, the GPON supports GEM (GPON Encapsulation Method) which deals with packets having a variable length like TDM (Time Division Multiplex) and Ethernet services (called ‘GEM’). At this time, the ATM maps transmission data into GTC frames with a cell unit to transfer the transmission data. Also, the GEM maps transmission data into GTC frames with a frame unit to transfer the transmission data.
FIG. 2 shows a protocol stack structure in a conventional GPON. Referring to FIG. 2, a protocol stack in the GPON includes a protocol layer 100 for interfacing with an upper layer, a GTC layer 200, and a GPM (GPON Physical Media dependent) layer 300. The protocol layer 100 includes an ATM (Asynchronous Transfer Mode) client 110, an OMCI (ONT Management Control Interface) 120, a GEM client 130, and a PLOAM (Physical Layer Operation Administration Maintenance) module 140.
The protocol stack of the GPON having the above structure multiplexes frames delivered from the upper layer into the GTC frames in the GTC layer 200 to transfer the multiplexed frames. In addition, the ATM client 110 supports a transmission method of the ATM. The GEM client 130 supports a transmission method of the GEM.
The ATM client 110 maps transmission data into the GTC frames with a fixed-length cell unit using the ATM. At this time, even though a space having a length smaller than a cell length (generally, 53 bytes) remains within the GTC frames, the transmission data are transferred by mapping the transmission data into a next frame. Accordingly, in a case of the ATM, cells are not divided.
However, when the GEM client 130 maps GEM frames into the GTC frames, since the GEM frames are packets having a variable length, the GEM client 130 may divide the GEM frames to transfer the divided GEM frames in order to efficiently use a bandwidth.
For example, the GEM client 130 receives space information (e.g., length) of currently-waiting GTC frames from the GTC layer 200 when the GEM client 130 receives user data from the upper layer. The GEM client 130 may divide the user data into a plurality of GEM frames, or can make one GEM frame without dividing the user data on the basis of space information. Thereafter, the GEM client 130 transfers the GEM frames to the GTC layer 200. The GTC layer 200 maps the GEM frames into the currently-waiting GTC frames to transfer the GEM frames.
Meanwhile, a receiving side transfers the GEM frames divided as mentioned above to the upper layer after assembling the divided GEM frames in the GEM layer 20.
Conventionally, an ONT management control protocol is provided for the BPON. The BPON operates on the basis of the ATM as suggested in G.983.1 series. Also, G.983.2 series suggests that an ONT management control interface of the BPON. The ONT management control interface of the BPON also operates on the basis of the ATM. In addition, the G.983.2 series suggests that a structure of a frame based on ATM cells which deliver management control information.
FIG. 3 illustrates the structure of the frame for delivering BPON ONT management control information that is suggested in the G.983.2. Hereinafter, fields included in the frame will be described in detail.
First, an ATM header 301 represents the VPI (Virtual Path Identifier)/VCI (Virtual Channel Identifier) values which are channel addresses used for management control.
A transaction correlation identifier 302 represents a relation between a request message and a response message.
A message type 303 represents a sort of a message.
A device identifier 304 represents a system based on ITU-T G.983.1 (OxOA).
A message identifier 305 represents both “managed entity” and “managed entity instance”.
Message contents 306 represent contents of messages defined by the message type 303.
FIG. 4 illustrates a conventional structure of a GEM frame supporting the TDM and the Ethernet services. The structure of the conventional GEM frame is defined in order to support a TDM frame or an Ethernet frame.
Referring to FIG. 4, the conventional GEM frame includes PLI(L) (16 bits) 410, Port ID (12 bits) 420, Frag (2 bits) 430, FFS (2 bits) 440, HEC (16 bits) 450, and Fragment Payload (L bytes) 460.
The PLI (Payload Length Identifier) 410, the Port ID 420, the Frag 430, the FFS 440, and the HEC 450 are included in a GEM header.
The PLI 410 represents a payload length. The Port ID 420 represents an ID for discriminating traffics in order to provide traffic multiplexing. The Frag 430 represents a division state of a payload. HEC 450 is a field for a header error detection and a header error correction. Meanwhile, the FFS 440 is a reserved field.
The Frag 430 included in the conventional GEM frame header represents whether or not a currently-transferred GEM payload is a divided frame by using 2 bits thereof. For instance, the GEM frame, which i s not divided, is represented by setting the Frag 430 as ‘11’. If the GEM frame has been divided, a start frame of the GEM frame, which has been divided. is represented by setting the Frag 430 as ‘10’, a middle frame of the GEM frame, which has been divided, is represented by setting the Frag 430 as ‘00’, and the last frame of the divided GEM frame, which has been divided, is represented by setting the Frag 430 as ‘01’. Accordingly, the Frag 430 represents whether or not the GEM frame has been divided. Also, if the GEM frame has been divided, the Frag 430 represents a position of a divided GEM frame in the GEM frame.
Meanwhile, an OLT makes communication with a plurality of the ONTs (ONUs) in the GPON that is being standardized in ITU-T. At this point in time, the OLT can support both ATM and GEM, or any one of both ATM and GEM to transfer data. However, ITU-T suggests in such a manner that the ONTs (ONUs) support only one mode of both ATM and GEM. In addition, the OLT requires the ONT management control interface in order to manage the ONTs (ONUs) connected thereto for communication. Therefore, the ONT management control interface must support the different transmission modes because the OLT may make communication with the ONTs (ONUs) by using different transmission modes from each other.
However, the protocol for the ONT management control interface, which is suggested in the G.983.2, is performed on the basis of the ATM. Accordingly, ONT management control packets are transferred by using the ATM cells of 53 bytes (refer to FIG. 3). At this time, the ATM header represents the VPI/VCI values which are channel addresses for the ONT management control interface. Also, information such as the Transaction Correlation Identifier 302, the Message Type 303, the Device Identifier 304, the Message Identifier 305, the Message Contents 306, and an ATM trailer 307 are delivered through an ATM cell payload. Accordingly, the ONTs (ONUs), which operate by using the ATM, can use the ONT management control interface suggested by the G.983.2.
However, there is a problem in that an ONT management control interface of the GEM and an ONT management control interface of the ATM are defined separately in the GPON. Accordingly, ONTs (ONUs) which operates by using the GEM cannot use the ONT management control interface of the ATM.
Accordingly, an ONT management control packet structure based on the GEM frame which can support ONT management control information must be defined in the GEM. That is, there is a need for a method for delivering control information must be considered in GEM protocol.